Heavy vehicles such as tractors, earth movers, and the like are provided with a roll-over protective structure which must be sturdy enough that it does not collapse in an ordinary overturning accident. Such structures ordinarily have four heavy corner posts which support a top frame and canopy above the operator's seat.
The extreme rigidity of hollow square posts makes them particularly desirable for use in such roll-over protection structures, and conveniently such posts have their lower end telescoped over upright, square mounting stubs on the vehicle and are secured to the stubs by bolts which impale the posts and the stubs.
The substantial motor vibration of such heavy vehicles is transmitted through the mounting stubs and the hollow posts into the canopy structure which vibrates and is excessively noisy unless vibration damping means is positioned within the posts. Heretofore such vibration damping means has taken the form of a hollow square member of elastomeric material which is seated upon a circumferential shoulder at the upper end of the stub and snugly surrounds an upper stub extremity which is of reduced cross-sectional area. The sides of the elastomeric member bear upon the inner surfaces of the walls of the hollow post so as to damp vibration which would otherwise be transmitted freely the length of the post.
Square posts which are formed from heavy gauge steel commonly have concave sides due to internal stresses produced during fabrication. A vibration damping member which is of such dimensions that it should fit comfortably within a particular post often binds so badly between the concave sides that the canopy posts must be forced upon the supporting stubs. This can produce damage to the damping member which hampers its effectiveness in suppressing vibration and noise, and which also may cause premature failure of the damping member.